The present invention relates to a radiation imaging apparatus and a radiographing method for the radiation imaging apparatus.
Hitherto, radiation images, represented by X-ray images, are widely used for medical diagnosis, and X-ray imaging apparatus are known as apparatus for effecting the X-ray images.
The X-ray imaging apparatus generally use an X-ray film as an X-ray detector to detect the X-rays having penetrated a subject, but in recent years, a flat panel detector (hereinafter referred to as FPD) which can change detected X-rays to electrical signals has been proposed.
FPDs are commonly composed of an X-ray/fluorescence conversion layer that converts the X-rays to fluorescent light,
a photoelectric conversion layer, located under the X-ray/fluorescence conversion layer, which detects the fluorescence that is converted by the X-ray/fluorescence conversion layer, and converts the fluorescence to electrical signals, and a glass base plate, located under the photoelectric conversion layer, of a predetermined thickness.
The X-ray/fluorescence conversion layer is the one in which fluorescent substance crystals used for a screen film (S/F), for example, are structured as a flat. The fluorescent substance has the nature to radiate the fluorescence proportional to the intensity of the X-rays that are radiated by the X-ray radiating apparatus which they penetrate the subject.
On the other hand, the photoelectric conversion layer is the one in which a number of imaging elements are arranged as a matrix, and is composed of light receiving sections such as light receiving sensors which detect the fluorescence converted from the X-rays, and switching sections such as TFTs (thin film transistors) which perform switching of the read-out performed by an electrical signal read-out device of the electrical signal outputted from the light receiving section.
Incidentally, the light receiving section and the switching section are formed from semiconductors such as amorphous silicone, and arranged adjacent to each other on the glass base plate. Further, the top of the light receiving section is a surface (hereinafter referred to as a light receiving surface) for receiving light.
Still further, there is another type of FPD that has not X-ray/fluorescence conversion layer, but has an X-ray/electrical signal conversion layer having an X-ray receiving section that directly converts the irradiated X-rays to electrical signals. Under the structure mentioned above, the top of the X-ray receiving section is the surface for receiving the X-rays (hereinafter referred to as an X-ray receiving surface), which has the same structure as the above-mentioned light receiving section.
Incidentally, electrical signals are read out by an electrical signal read-out device, and are converted to digital image data by an A/D converter, which are stored in a memory device (not illustrated).
Incidentally, when X-ray radiography is performed, it is necessary to perform a so-called slanting radiograph based on the radiographing region, that is, the radiating angle of the X-rays to the radiographing region is set to be slanted from a right angle.
However, for FPDs having an X-ray/fluorescence conversion layer, the height of the surface which receives light is less than that of the switching section, and accordingly, when the slanting radiography is effected, some of the light receiving surface is shaded by the switching section, and an amount of the light rays received by the light receiving surface becomes less.
Further, for FPDs having an X-ray/electrical signal conversion layer instead of the X-ray/fluorescence conversion layer, the height of the X-ray receiving surface is less than that of the switching section, and when the slanting radiography is effected, a part of the X-ray receiving surface is shaded by the switching section, and accordingly, the amount of the X-rays received by the X-ray receiving surface becomes less.
Due to this, the quality of the X-ray images formed by the slanting radiography is reduced.